The overall objective is to determine the intraovarian and extraovarian endocrine relationships which govern ovarian function during pregnancy in the rabbit and rat. The functional significance of aromatization in the rat corpus luteum will be investigated with particular attention to the role of intraluteal estradiol in the regulation of progesterone synthesis in the corpus luteum. The mechanism of luteinization of Graafian follicles will be investigated using a procedure in which follicles are incubated in vitro and autotransplanted beneath the kidney capsule where they develop into ectopic corpora lutea. Follicles will be incubated with 125I-hCG to determine the site of binding of labeled hormone and the role of hormone binding in subsequent luteinization. The contribution and functional significance of theca internal cells during luteinization will be studied by histologic and autoradiographic analysis of copora lutea derived from follicles with "tagged" thecal cells and by transplantation of isolated follicular cells.